Effect of circulating IgG antibody on the uptake of enteric antigen is being investigated in neonatal rabbits. In these experiments female New Zealand White rabbits are immunized with bovine serum albumin. After obtaining serum, all infant rabbits born to these immunized rabbits as well as litter mates from non-immunized female rabbits were gavaged with l00 mg of 125I trace labelled BSA. The fed animals are sacrificed at various time intervals and sera, drawn from the heart and from the portal circulation, are examined for intact antigen by electroimmunodiffusion. In separate experiments litters from New Zealand White rabbits which have been passively immunized with anti-BSA antibody from immunized mothers, are examined in the following manner. l00 mg of cold BSA is fed by gavage to half the animals. The remaining infant rabbits received l00 mg of fibrinogen by gavage. One hour later all animals receive a gavage feed of l00 mg of egg albumin. Four hours after the egg albumin gavage serum is drawn from the heart and examined for the presence of egg albumin and BSA. It is expected that the antigen-antibody interaction which occurs in the small intestine in immunized animals will affect the absorption of a bystander antigen present at the same time in the small intestine.